Method of cleaning products to which dirt adheres

ABSTRACT

Solid products to which dirt adheres are cleaned by introducing them into a container filled with water, mechanically transporting the products through the container to form in the container a suspension of sludge in the water, the sludge comprising dirt which has been removed from the products, the sludge having a specific mass that approaches the specific mass of water. A stream of finely divided air bubbles is fed through the sludge suspension in the container thereby to lower the specific mass of the water and to cause sludge to move by gravity toward a lower section of the container. Sludge-enriched water is removed from that lower section of the container. The products are mechanically transported by a conveyor into and through and out of the container after dirt has been removed therefrom.

This is a national stage application of PCT/NL98/00467 filed Aug. 8,1998.

FIELD OF THE INVENTION

The present invention relates to a method for separating sludge-likematerial and water, said sludge-like material hang a specific mass thatapproaches the specific mass of water, in which method a suspension,comprising water and sludge, is moved through a container.

BACKGROUND OF THE INVENTION

A method of this type is generally known in the prior art. The aim is tocause the sludge-like material to float to the top with the aid offlotation techniques and the material that is forced up is skimmed offwith the aid of skimming equipment. Separate foaming agents and the likeare needed for this purpose. The addition of said agents not only incurscosts, but frequently gives rise to farther contamination of the water,

Other methods for separating sludge-like material and water compriseheating, as a result of which water is removed by evaporation andsludge-like material remains behind. A method of this type isparticularly energy-intensive and has been proposed, for example, forconcentrating manure-like materials.

From the Japanese patent application 57094388 a method is known tosuppress and prevent the floating and concentrating of sludge. Removalof anaerobic gas is realised by subjecting sludge to flow of air. Afteraeration sludge is bent to a separate container for further processing.

OBJECT OF THE INVENTION

The aim of the present invention is to provide a method with which waterand sludge-like material are essentially separated from one anotherwithout further chemicals or highly energy-intensive steps beingrequired for this purpose.

SUMMARY OF THE INVENTION

This aim is achieved with a method as described in that a verticallyascending steam of finely divided air bubbles is fed through the sludgesuspension in the container and in that a stream containingsludge-enriched fluid is drained from the lower section of thecontainer.

The insight on which the invention is based is, in contrast to the priorart, not to make use of flotation for the sludge-like material but tolower the apparent specific mass of water by feeding in air, as a resultof which settling of sludge takes place because the specific mass of thesludge is then higher. The sludge can then be discharged.

The method described above can be used, inter alia, for concentratingmanure-like materials.

However, surprisingly it has been found that the method can also be usedfor cleaning products such as (flower) bulbs. Soil material alwaysadheres to bulbs of this type and for export to certain countries theregulations lay down that there must be absolutely no soil materialadhering to such bulbs. For this purpose, in the prior art, the bulbsare subjected to a spray-treatment with water under high pressure.Damage to the bulbs regularly occurs as a result and there is noguarantee that grains of sand and the like have also been completelyremoved from the bulbs.

Another method for cleaning bulbs is to introduce them into drums oflarge diameter, for example having a capacity of 15 m³. These bulbs,such as lily bulbs, are cleaned using a sort of washing machinetreatment. However, the sand present in water damages the bulb byetching into it. Moreover, this method produces large quantities ofwaste water for which there is no further use. Discharge is becomingincreasingly less acceptable under current conditions.

By now feeding the bulbs, which, including the earth adhering thereto,have a specific mass that approaches the specific mass of water, througha bath in which rising air is moving, any soil material adhering to thebulbs is detached in a very gentle manner and brought into suspensionand sludge material of this type precipitates by means of the mechanismdescribed above.

It is possible to subject the sludge-enriched fluid to a furthercorresponding treatment, that is to say to pass it again through a bathwith an air stream, as a result of which further concentration of thematerial can take place.

The invention also relates to a device for separating sludge-likematerial and water, comprising a container to be filled with water,which container is provided with feed means for said sludge-containingmaterial.

According to the invention, the base of the container is provided withfeed means for air, comprising perforated air feed elements, and adischarge for sludge arranged above these.

The device will be of different construction depending on theapplication of the method described above. When cleaning bulbs or otherproducts, such products will be fed with the aid of a conveyor belt intoa container which contains water or another suitable fluid. Air ispassed through the container and the resulting deposit is discharged.The products are then removed from the container, likewise by mechanicalmeans.

If, for example, manure has to be concentrated, it is not necessary toremove products from the container. After all, in this case there are,in principle, two waste streams, one containing concentrated sludge andthe other containing treated fluid, such as water. However, it ispossible to carry out a number of treatment steps and this is importantespecially in the case of the concentration of sludge-like materials.According to the invention, an assembly comprising a number of deviceslocated downstream of one another in the direction of flow is proposedfor this purpose.

Essentially the same quantity of water can still be used with the methodnow proposed. The quantity of moisture in the discharge sludge isrelatively small. Consequently, small quantities of waste water areproduced, which appreciably reduces the problems associated withcleaning. Pre-treatment and after-treatment devices can be locatedupstream and downstream of the device according to the invention. Anexample of a pre-treatment device which may be mentioned is a vacuumchamber with which adhering porous parts are detached. Anafter-treatment device can be a separator device in order to enable theused rinsing water to be recycled. An (infra red) drying device for thecrop can also be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toillustrative embodiments shown in the drawings. In the drawings:

FIG. 1 shows, diagrammatically, a side view of a device for cleaningharvested bulbs; and

FIG. 2 shows, diagrammatically, a side view of a device forconcentrating manure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a device for cleaning bulbs. Said device is indicated inits entirety by 1. A conveyor 2 is fitted, onto which bulbs, indicateddiagrammatically by 5, are placed via a feed 3. Conveyor 2 is providedwith partitions 4 in order to hold the bulbs as far as possible inplace, especially in the descending and ascending section of theconveyor. In the conveyor part 12 of conveyor 2 the bulbs are thenintroduced into a container 6. The latter is filled with water 7. Thereis a perforated base 8 in the underside of the container.

The perforated base is provided with perforations having a diameter ofbetween 10 and 60 μm and more particularly 20 and 30 μm. The perforatedplate can be made of stainless steel or plastic. Beneath the perforatedplate there is a chamber through which air is introduced via feed 9. Theair rises, as indicated by arrows 11, upwards through the perforatedplate 8. Just above the perforated plate there is a discharge 14 forsludge. In a variant it is possible that the first section of theconveyor 2 is also below water level. By this means the fall of the croponto the conveyor is softened by the water.

The bulbs, which are on the conveyor part 12, then move out of thecontainer 6 and are deposited in collection bin 10.

The device described above functions as follows:

On movement of the bulbs, to which earth is adhering, in trough orcontainer 6, said soil particles will be soaked gently away from thebulbs by the rising fine air bubbles. Because the specific mass of thewater is relatively low as a result of the presence of air, the soilparticles will immediately sediment out and be moved towards discharge14 by the partitions 4 which are moving in the return part 13 of theconveyor 2. In this way, on the one hand, the bulbs are cleaned and, onthe other hand, sludge is removed from the contaminated water.

FIG. 2 shows a second application of the method according to theinvention. The assembly shown in this figure is indicated in itsentirety by 21. The assembly consists of a feed conveyor 23 and a numberof linked separating chambers 24-27 arranged downstream thereof incascade form. A screen 28 is fitted in each separating chamber. Thescreen has approximately the same characteristics as the perforatedplate or screen 8. An air feed 29 is fitted below each screen. Asplitter plate 30 is located in the lowest section of each separatingchamber. The splitter plate 30 can have a fixed position or can beadjustable in height in order to vary the height with respect to thescreen 28.

31 shows the path of the rising gas bubbles, originating from air feed29.

Plate 30 provides for separation between sludge of relatively highspecific mass (the underside) and relatively clean water, which isdischarged via clean water discharge 32 to drain point 33. Arrow 36indicates the direction of the discharged sludge.

There is a discharge conveyor 34, that emerges in container 35, for therelatively heavier sludge.

The device described above functions as follows:

A material to be cleaned, such as sludge, manure and the like, thatcontains a large proportion of water, is placed on feed conveyor 23 andthe material is fed into the first chamber 24. The apparent specificmass of water is lowered by the rising gas bubbles, as a result of whichthe sludge settles out of the suspension with water and moves, inaccordance with arrow 36, over the perforated plate 28 beneath plate 30to chamber 25. The relatively cleaner water is fed directly to the cleanwater discharge 32. The same operation takes place in chamber 25,further concentration of sludge taking place. The same applies in thecase of chambers 26 and 27. In this way concentration of the sludgematerial can take place without energy-intensive measures and withoutthe supply of chemicals. The air supply can be achieved at relativelylow pressure. In practice it has been found that adequate air can betransported through the water using a simple fan of relatively lowpower.

For those skilled in the art it will be immediately apparent from thecompletely different set-ups in the illustrative embodiments describedabove that numerous variants of the inventive concept are possiblewithout going beyond the scope of the present application. Thus, forexample, it is possible in the variant according to FIG. 2 to make theangle between the various chambers adjustable depending on the materialto be processed. Furthermore, a wide variety of products can be treated,such as other agricultural products but, for example, alsoarchaeological finds which have to be treated very carefully. It istherefore also intended that variants of this type fall within theinventive concept, as formulated in the appended claims.

What is claimed is:
 1. A method of cleaning products to which dirtadheres, consisting of introducing said products into a container filledwith water; transporting said products through the container to form inthe container a suspension of sludge in said water, said sludgecomprising dirt which has been removed from the products, said sludgehaving a specific mass that approaches the specific mass of water;feeding a stream of finely divided air bubbles through the sludgesuspension in the container thereby to lower the specific mass of thewater relative to the specific mass of the sludge whereupon the sludgemoves toward a lower section of said container; removing sludge-enrichedwater from said lower section of said container; and transporting saidproducts out of the container after dirt has been removed therefrom. 2.The method as claimed in claim 1, and further treating saidsludge-enriched water to separate sludge therefrom.